1. Field of the Invention
The present invention pertains to transducers useful for acoustic type wellbore logging tools which are responsive to fluid displacements in a well bore to produce an electrical signal or vice versa utilizing the phenomena of the Lorentz force.
2. Background
In the development of acoustic logging tools and similar acoustic signal transmitting and receiving apparatus, several types of signal transmitting and receiving transducers have been developed. One type of transducer which relies on the phenomena associated with piezoelectric materials is described in U.S. Pat. No. 4,649,525 to Angona, et al. Certain improvements in transducers which utilize piezoelectric elements are described in U.S. Pat. No. 4,975,615, issued Dec. 4, 1990, to Keith W. Katahara, Ser. No. 07/354,067, filed May 17, 1989, to Steven G. Peterman, et al, and U.S. Pat. No. 4,949,316 issued Aug. 14, 1990, to Keith W. Katahara, all assigned to the assignee of the present invention.
The tranducers described in the abovementioned patent and patent applications are suitable for certain applications but have limitations as to frequency bandwidth sensitivity. Typically, these transducers offer good sensitivity at or near their resonant frequencies but have poor sensitivity in other ranges which are desirable for use in wellbore logging tools and certain other applications. On the other hand, certain types of transducers, which have very broad band response, such as described in U.S. patent application Ser. No. 07/319,607, filed Mar. 6, 1989, to Keith W. Katahara and assigned to the assignee of the present invention, cannot be readily used as a receiving type transducer but are more desirable for use as signal generating transducers. Accordingly, there has been a need for the development of a type of transducer which has relatively broad frequency bandwidth response, when operating as a receiver or a transmitter, and is structurally uncomplicated.